Elastic wave devices, filters, and multiplexers

Abstract

The present invention provides elastic wave devices, filters, and multiplexers capable of improving power handling. [Solution] The elastic wave device comprises a piezoelectric layer 15, a first layer 31 provided on the piezoelectric layer 15 which is a titanium aluminum nitride layer, a chromium aluminum nitride layer, a chromium nitride layer, a diamond-like carbon layer, or a titanium carbide nitride layer, and a second layer 32 provided on the first layer 31 which is a metal layer formed of a metal with a lower electrical resistivity than the first layer 31, and includes a pair of comb-shaped electrodes 22 including electrode fingers 23.

Description

Technical Field

[0001] The present invention relates to an elastic wave device, a filter, and a multiplexer.

Background Art

[0002] In a high-frequency communication system typified by a mobile phone, a high-frequency filter is used to remove unnecessary signals outside the frequency band used for communication. For example, a surface acoustic wave (SAW) resonator is used in the high-frequency filter. In the surface acoustic wave resonator, an interdigital transducer (IDT) having a plurality of electrode fingers is provided on a piezoelectric layer such as a lithium tantalate layer or a lithium niobate layer. It is known to use an aluminum layer or an aluminum alloy layer as the electrode fingers (for example, Patent Documents 1-2). Also, in a capacitor in which a buffer layer, a dielectric layer, and an electrode are laminated, it is known to use a titanium aluminum nitride layer for the buffer layer (for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the electrode fingers, it is known that the withstand voltage can be improved by providing a titanium layer between the piezoelectric layer and a low-resistance metal layer such as aluminum. However, there is still room for improvement in terms of improving the withstand voltage.

[0005] This invention has been made in view of the above problems and aims to improve power resistance. [Means for solving the problem]

[0006] The present invention is an elastic wave device comprising a pair of comb-shaped electrodes including electrode fingers, each having a piezoelectric layer, a first layer provided on the piezoelectric layer which is a titanium aluminum nitride layer, a chromium aluminum nitride layer, a chromium nitride layer, a diamond-like carbon layer, or a titanium carbide nitride layer, and a second layer provided on the first layer which is a metal layer formed of a metal with a lower electrical resistivity than the first layer.

[0007] In the above configuration, the first layer is a titanium aluminum nitride layer, and the proportion of aluminum atoms is 20% or more and 50% or less when the total amount of titanium atoms and aluminum atoms is 100%.

[0008] In the above configuration, the first layer is a titanium aluminum nitride layer, and the proportion of nitrogen atoms is 10 atomic percent or more when the total amount of titanium atoms, aluminum atoms, and nitrogen atoms is 100 atomic percent.

[0009] In the above configuration, the second layer can be an aluminum layer, an aluminum alloy layer, a copper layer, or a copper alloy layer.

[0010] In the above configuration, the thickness of the first layer can be 5% or more and 60% or less of the thickness of the electrode finger.

[0011] In the above configuration, the electrode finger has a third layer between the first and second layers that is thinner than the first and second layers, the second layer being an aluminum layer, an aluminum alloy layer, a copper layer, or a copper alloy layer, and the third layer being a titanium layer or a titanium nitride layer.

[0012] The present invention is a filter that includes the elastic wave device described above.

[0013] The present invention is a multiplexer including the filter described above.

Advantages of the Invention

[0014] According to the present invention, the power resistance can be improved.

Brief Description of the Drawings

[0015] [Figure 1] Fig. 1(a) is a plan view of the surface acoustic wave device according to Example 1, and Fig. 1(b) is a cross-sectional view of the electrode fingers in Example 1. [Figure 2] Figs. 2(a) to 2(d) are cross-sectional views of the surface acoustic wave resonators of Samples A to D used in the experiment. [Figure 3] Fig. 3 is a diagram showing the results of the power resistance test of the surface acoustic wave resonators of Samples A to D. [Figure 4] Fig. 4 is a diagram showing the measurement results of the frequency temperature characteristics (TCF: Temperature Coefficient of Frequency) of the anti-resonance frequencies of the surface acoustic wave resonators of Samples A to D. [Figure 5] Fig. 5 is a cross-sectional view of the surface acoustic wave device according to Modification 1 of Example 1. [Figure 6] Figs. 6(a) to 6(e) are cross-sectional views of the surface acoustic wave devices according to Modifications 2 to 6 of Example 1. [Figure 7] Figs. 7(a) and 7(b) are cross-sectional views of the surface acoustic wave devices according to Modifications 7 and 8 of Example 1. [Figure 8] Fig. 8 is a binary phase diagram of titanium and aluminum. [Figure 9] Fig. 9(a) is a circuit diagram of the filter according to Example 3, and Fig. 9(b) is a circuit diagram of the diplexer according to the modification of Example 3.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Examples]

[0017] Figure 1(a) is a plan view of the elastic wave device 100 according to Example 1, and Figure 1(b) is a cross-sectional view of the electrode fingers 23 in Example 1. The arrangement direction of the electrode fingers 23 is the X direction, the extension direction of the electrode fingers 23 is the Y direction, and the thickness direction of the piezoelectric layer 15 is the Z direction. The X, Y, and Z directions do not necessarily correspond to the X-axis and Y-axis directions of the crystal orientation of the piezoelectric layer 15. If the piezoelectric layer 15 is a piezoelectric layer with rotational Y-cut X propagation, the X direction is the X-axis direction of the crystal orientation.

[0018] As shown in Figure 1(a), an elastic wave resonator 20 is provided on the piezoelectric layer 15. In Example 1, the piezoelectric layer 15 is a piezoelectric substrate. The piezoelectric layer 15 is formed of, for example, single-crystal lithium tantalate, single-crystal lithium niobate, or quartz. The piezoelectric layer 15 may be, for example, a rotating Y-cut X-propagating lithium tantalate layer or a rotating Y-cut X-propagating lithium niobate layer, or for example, a 30°~50° rotating Y-cut X-propagating lithium tantalate layer. The elastic wave resonator 20 has an IDT (Interdigital Transducer) 21 and a reflector 25. The reflector 25 is provided on both sides of the IDT 21 in the X direction. The IDT 21 comprises a pair of opposing comb-shaped electrodes 22. The comb-shaped electrodes 22 comprise a plurality of electrode fingers 23 and a busbar 24 to which the plurality of electrode fingers 23 are connected. The region where the electrode fingers 23 of the pair of comb-shaped electrodes 22 intersect is the intersection region 26. The length of the intersection region 26 in the Y direction is the opening length.

[0019] The pair of comb-shaped electrodes 22 have alternating electrode fingers 23, one at a time, in at least a portion of the intersection region 26. The elastic wave that primarily excites the multiple electrode fingers 23 in the intersection region 26 propagates mainly in the X direction. The pitch of the electrode fingers 23 of one of the pair of comb-shaped electrodes 22 is approximately equal to the wavelength λ of the elastic wave. The wavelength λ is approximately twice the average pitch D of the multiple electrode fingers 23. The average pitch D can be calculated by dividing the length of the IDT 21 in the X direction by the number of electrode fingers 23. The reflector 25 reflects the elastic wave (surface acoustic wave) excited by the electrode fingers 23 of the IDT 21. As a result, the elastic wave is confined within the intersection region 26 of the IDT 21.

[0020] As shown in Figure 1(b), the IDT 21, such as the electrode fingers 23, and the reflector 25 are formed by a conductive film 30 provided on the piezoelectric layer 15. The conductive film 30 comprises a first layer 31 provided on the piezoelectric layer 15 and a second layer 32 provided in contact with the upper surface of the first layer 31. The thicknesses of the first layer 31 and the second layer 32 are T1 and T2, respectively. The thickness of the conductive film 30 is T3. T3 = T1 + T2.

[0021] The first layer 31 is a titanium aluminum nitride (TiAlN) layer, is conductive, and is polycrystalline or amorphous. The first layer 31 may contain impurities other than titanium (Ti), aluminum (Al), and nitrogen (N), either intentionally or unintentionally. For example, in the first layer 31, the proportion of aluminum atoms is between 20 atomic% and 50 atomic% when the total amount of titanium atoms and aluminum atoms is 100 atomic%. Also, in the first layer 31, the proportion of nitrogen atoms is between 10 atomic% and 60 atomic% when the total amount of titanium atoms, aluminum atoms, and nitrogen atoms is 100 atomic%. The atomic concentration can be measured using, for example, secondary ion mass spectrometry or Auger electron spectroscopy. The thickness T1 of the first layer 31 varies depending on the operating band in which the elastic wave device 100 is used. For example, it is 120 nm to 300 nm when used in the low band (less than 1 GHz), 30 nm to 90 nm when used in the middle band (1 GHz to 7 GHz), and 5 nm to 60 nm when used in the high band (greater than 7 GHz). The thickness T1 of the first layer 31 may also be, for example, 5% to 60% of the thickness T3 of the electrode finger 23.

[0022] The second layer 32 is, for example, an aluminum layer (Al layer) or an aluminum alloy layer (Al alloy layer), and is, for example, polycrystalline or amorphous. If the second layer 32 is an aluminum alloy layer, the second layer 32 contains at least one element other than aluminum (Al) from among copper (Cu), magnesium (Mg), scandium (Sc), zirconium (Zr), titanium (Ti), neodymium (Nd), and silicon (Si). If the second layer 32 is an aluminum layer, the second layer 32 may contain impurities other than aluminum, intentionally or unintentionally. If the second layer 32 is an aluminum alloy layer, the second layer 32 may contain impurities other than aluminum and the metallic elements constituting the aluminum alloy, intentionally or unintentionally. The aluminum content in the second layer 32 is, for example, 80 atomic% or more, and 90 atomic% or more. The thickness T2 of the second layer 32 may be greater than the thickness T1 of the first layer 31. The thickness T2 of the second layer 32 varies depending on the operating band in which the elastic wave device 100 is used. For example, it is 150 nm to 350 nm when used in the low band (less than 1 GHz), 100 nm to 200 nm when used in the middle band (1 GHz to 7 GHz), and 80 nm to 120 nm when used in the high band (greater than 7 GHz). The thickness T2 of the second layer 32 may also be, for example, 40% to 95% of the thickness T3 of the electrode finger 23.

[0023] [Manufacturing method] The elastic wave device 100 according to Example 1 is manufactured by the following method. First, a first layer 31, which is a TiAlN layer, is deposited on the piezoelectric layer 15. For example, the first layer 31 is deposited by a sputtering method using a titanium aluminum (TiAl) alloy target, argon (Ar) gas, and nitrogen (N2) gas. The nitrogen content can be adjusted by adjusting the flow rate of the N2 gas. The Ti and Al content can be adjusted by changing the ratio of Ti and Al in the TiAl alloy target.

[0024] Next, a second layer 32, which is an Al layer or an Al alloy layer, is deposited on the first layer 31. For example, if the second layer 32 is an Al layer, the second layer 32 is deposited by a sputtering method using an Al target and Ar gas. If the second layer 32 is an Al alloy layer, the second layer 32 is deposited by a sputtering method using an Al alloy target, which is aluminum with other elements added, and Ar gas.

[0025] Next, the first layer 31 and the second layer 32 are shaped into the desired form using photolithography and etching to form the IDT 21 and the reflector 25. Thus, the elastic wave device 100 according to Example 1 is formed.

[0026] [experiment] Figures 2(a) to 2(d) are cross-sectional views of the elastic wave resonators of samples A to D used in the experiment. In samples A to D, a 42° rotated Y-cut X-propagating lithium tantalate layer was used for the piezoelectric layer 15. As shown in Figure 2(a), in the elastic wave resonator of sample A, the IDT 21 such as the electrode fingers 23 and the reflector 25 were formed from a conductive film 45a consisting of a titanium layer 40 and an aluminum-copper alloy layer 44. The thickness of the titanium layer 40 was 60 nm, and the thickness of the aluminum-copper alloy layer 44 was 90 nm. The wavelength λ(2×D) of the elastic wave was 1.5 μm.

[0027] As shown in Figure 2(b), in the elastic wave resonator of sample B, the IDT 21, such as the electrode fingers 23, and the reflector 25 were formed from a conductive film 45b consisting of a titanium-aluminum alloy layer 41 (TiAl alloy layer) and an aluminum-copper alloy layer 44. The titanium-aluminum alloy layer 41 had an aluminum atom content of 36 atomic percent when the total amount of titanium and aluminum atoms was 100 atomic percent. The thickness of the titanium-aluminum alloy layer 41 was 60 nm, and the thickness of the aluminum-copper alloy layer 44 was 90 nm. The wavelength of the elastic wave λ(2×D) was 1.5 μm.

[0028] As shown in Figure 2(c), in the elastic wave resonator of sample C, the IDT 21, such as the electrode fingers 23, and the reflector 25 were formed from a conductive film 45c consisting of a titanium nitride layer 42 and an aluminum-copper alloy layer 44. The thickness of the titanium nitride layer 42 was 60 nm, and the thickness of the aluminum-copper alloy layer 44 was 90 nm. The wavelength λ(2×D) of the elastic wave was 1.5 μm.

[0029] As shown in Figure 2(d), in the elastic wave resonator of sample D, the IDT 21, such as the electrode fingers 23, and the reflector 25 were formed from a conductive film 45d consisting of a titanium aluminum nitride layer 43 (TiAlN layer) and an aluminum copper alloy layer 44. The titanium aluminum nitride layer 43 had an aluminum atom content of 36 atomic percent when the total amount of titanium atoms and aluminum atoms was set to 100 atomic percent. Also, the nitrogen atom content was set to 50 atomic percent when the total amount of titanium atoms, aluminum atoms, and nitrogen atoms was set to 100 atomic percent. The thickness of the titanium aluminum nitride layer 43 was 60 nm, and the thickness of the aluminum copper alloy layer 44 was 90 nm. The wavelength of the elastic wave λ(2×D) was 1.5 μm.

[0030] Withstand power tests were performed on elastic wave resonators of samples A to D. The withstand power tests employed the Step Stress Accelerated Life Test (SSALT) method, in which the applied power was gradually increased. Figure 3 shows the results of the withstand power tests for elastic wave resonators of samples A to D. In Figure 3, the horizontal axis represents the input power applied to the elastic wave resonator, and the vertical axis represents the insertion loss. As shown in Figure 3, samples A and B showed significant degradation in insertion loss even at relatively low input power levels. On the other hand, samples C and D both showed suppressed degradation of insertion loss even at high input power levels, but sample D showed even more suppressed degradation of insertion loss than sample C.

[0031] Observation of the surfaces of samples A to D after the power withstand test revealed that sample D showed less electromigration compared to samples A to C. This suggests that sample D's reduced electromigration improved its power withstand capability, thus minimizing the degradation of insertion loss.

[0032] Next, the frequency-temperature coefficient of frequency (TCF) of the anti-resonance frequencies of the elastic wave resonators of samples A to D was measured when the ambient temperature changed from 25°C to 85°C. Figure 4 shows the measured TCF results for the anti-resonance frequencies of the elastic wave resonators of samples A to D. As shown in Figure 4, the absolute value of the TCF for sample D was smaller than that of samples A to C.

[0033] Sample D shows improved power handling and TCF compared to Samples A-C. The reason for this improvement is not clear, but the following are possible explanations. Table 1 shows the results of measuring the resistance, density, and Young's modulus of each film after depositing a Ti layer (titanium layer), TiAl alloy layer (titanium aluminum alloy layer), TiN layer (titanium nitride layer), and TiAlN layer (titanium aluminum nitride layer) on a silicon substrate. The speed of sound was calculated using density and Young's modulus. The TiAl alloy layer measurement is for when the proportion of aluminum atoms is 36 atomic percent when the total amount of titanium atoms and aluminum atoms is 100 atomic percent. The TiAlN layer measurement is for when the proportion of aluminum atoms is 36 atomic percent when the total amount of titanium atoms and aluminum atoms is 100 atomic percent, and the proportion of nitrogen atoms is 50 atomic percent when the total amount of titanium atoms, aluminum atoms, and nitrogen atoms is 100 atomic percent. [Table 1]

[0034] As shown in Table 1, the Young's modulus of the TiAlN layer is larger than that of the Ti layer, TiAl alloy layer, and TiN layer. Since the electrode finger 23 of sample D uses a titanium aluminum nitride layer 43 (TiAlN layer), it is thought that the large Young's modulus of the titanium aluminum nitride layer 43 is one of the reasons for the improved power handling capacity and improved TCF. In other words, because the titanium aluminum nitride layer 43 with a large Young's modulus is provided as an underlayer for the aluminum copper alloy layer 44, it is thought that the aluminum copper alloy layer 44 is less likely to deform even when the electrode finger 23 is excited. As a result, it is thought that in sample D, the strain generated in the aluminum copper alloy layer 44 was reduced, electromigration was suppressed, and power handling capacity was improved. In addition, the Young's modulus of the materials constituting the electrode finger 23 changes with temperature, and is larger than the temperature change of the Young's modulus of the piezoelectric layer 15. Since the titanium aluminum nitride layer 43 has a large Young's modulus, even if the Young's modulus of the titanium aluminum nitride layer 43 and the aluminum copper alloy layer 44 changes with temperature, the titanium aluminum nitride layer 43 is less likely to deform, which is thought to have improved TCF. Furthermore, as shown in Table 1, the TiAlN layer has a high Young's modulus, resulting in a high speed of sound. When the high-speed titanium aluminum nitride layer 43 is provided as an underlayer for the aluminum-copper alloy layer 44, it is thought that more elastic wave energy is distributed in the piezoelectric layer 15. This is also thought to be the reason why the TCF of sample D was improved.

[0035] Based on the above experimental results, it can be seen that in Example 1, the electrode finger 23 is formed by a conductive film 30 which is a laminated first layer 31 which is a titanium aluminum nitride layer and a second layer 32 which is an aluminum layer or an aluminum alloy layer, and that this provides the effect of improving power resistance and TCF.

[0036] [Differentiation] Figure 5 is a cross-sectional view of the elastic wave device 110 according to Modification 1 of Example 1. As shown in Figure 5, in Modification 1 of Example 1, a third layer 33, which is a titanium layer or titanium nitride layer, is provided between the first layer 31 and the second layer 32. The thickness T4 of the third layer 33 is smaller than the thickness T1 of the first layer 31 and the thickness T2 of the second layer 32. When the third layer 33 is provided, the thickness T3 of the electrode finger 23 is T3 = T1 + T2 + T4. The other configurations are the same as in Example 1, so their explanation is omitted.

[0037] Figure 6(a) is a cross-sectional view of the elastic wave device 120 according to Modification 2 of Example 1. As shown in Figure 6(a), in Modification 2 of Example 1, the piezoelectric layer 15 is provided on the substrate 10. The other configurations are the same as in Example 1, so their description is omitted.

[0038] Figure 6(b) is a cross-sectional view of the elastic wave device 130 according to Modification 3 of Example 1. As shown in Figure 6(b), in Modification 3 of Example 1, the piezoelectric layer 15 is provided on the substrate 10. An insulating layer 12 is provided between the substrate 10 and the piezoelectric layer 15. An insulating layer 13 is provided between the insulating layer 12 and the piezoelectric layer 15. The interface between the substrate 10 and the insulating layer 12 is roughened. The other configurations are the same as in Example 1, so their description is omitted.

[0039] Figure 6(c) is a cross-sectional view of the elastic wave device 140 according to Modification 4 of Example 1. As shown in Figure 6(c), in Modification 4 of Example 1, the piezoelectric layer 15 is provided on the substrate 10. An insulating layer 11 is provided between the substrate 10 and the piezoelectric layer 15. An insulating layer 12 is provided between the insulating layer 11 and the piezoelectric layer 15. An insulating layer 13 is provided between the insulating layer 12 and the piezoelectric layer 15. The other configurations are the same as in Example 1, so their description is omitted.

[0040] Figure 6(d) is a cross-sectional view of the elastic wave device 150 according to Modification 5 of Example 1. In Modification 4 of Example 1, the interface between the substrate 10 and the insulating layer 11 was mirror-finished, as shown in Figure 6(c), but in Modification 5 of Example 1, the interface between the substrate 10 and the insulating layer 11 is roughened, as shown in Figure 6(d). The other configurations are the same as in Modification 4 of Example 1, so their explanation is omitted. The arithmetic mean roughness Ra of the roughened surface is, for example, greater than 10 nm and 100 nm or less, while the arithmetic mean roughness Ra of the mirror-finished surface is, for example, 10 nm or less and about 1 nm.

[0041] Figure 6(e) is a cross-sectional view of the elastic wave device 160 according to Modification 6 of Example 1. In Modifications 4 and 5 of Example 1, the interface between the insulating layer 11 and the insulating layer 12 was mirror-finished, as shown in Figures 6(c) and 6(d), but in Modification 6 of Example 1, the interface between the insulating layer 11 and the insulating layer 12 is roughened, as shown in Figure 6(e). The other configurations are the same as in Modification 5 of Example 1, so their description is omitted.

[0042] In Modifications 2 to 6 of Example 1, the substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, a silica substrate, or a silicon carbide substrate. The speed of sound of the bulk wave propagating through the substrate 10 may be faster or slower than the speed of sound of the bulk wave propagating from the piezoelectric layer 15 and the insulating layer 11 to the insulating layer 13.

[0043] In Modifications 4 to 6 of Example 1, the speed of sound of the bulk wave propagating through the insulating layer 11 is faster than the speed of sound of the bulk wave propagating through the insulating layer 12 and the piezoelectric layer 15. As a result, the energy of the main response elastic wave is confined within the piezoelectric layer 15 and the insulating layer 12. The insulating layer 11 is, for example, polycrystalline or amorphous, and is an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, a silicon layer, or a silicon carbide layer.

[0044] In Modifications 3 to 6 of Example 1, the insulating layer 12 is a temperature compensation layer and has a temperature coefficient of elasticity with the opposite sign to the sign of the temperature coefficient of elasticity of the piezoelectric layer 15. For example, the temperature coefficient of elasticity of the piezoelectric layer 15 is negative, and the temperature coefficient of elasticity of the insulating layer 12 is positive. The insulating layer 12 is an insulating layer mainly composed of silicon oxide, for example, a silicon oxide layer with no additives or containing additive elements such as fluorine, and for example, polycrystalline or amorphous. This makes it possible to reduce the frequency temperature coefficient of the elastic wave resonator. When the insulating layer 12 is a silicon oxide layer, the speed of sound of bulk waves propagating through the insulating layer 12 is slower than the speed of sound of bulk waves propagating through the piezoelectric layer 15.

[0045] The insulating layer 13 is a bonding layer that joins the insulating layer 12 and the piezoelectric layer 15. When the insulating layer 12 is a silicon oxide layer, it is difficult to directly bond the piezoelectric layer 15 and the insulating layer 12 using a surface activation method. In such cases, an insulating layer made of a different material from the insulating layer 12 is provided as the insulating layer 13. The insulating layer 13 is, for example, polycrystalline or amorphous, and is an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, a silicon layer, or a silicon carbide layer.

[0046] Figure 7(a) is a cross-sectional view of the elastic wave device 170 according to Modification 7 of Example 1. As shown in Figure 7(a), in Modification 7 of Example 1, a protective film 16 is provided on the piezoelectric layer 15 so as to cover the electrode fingers 23. The thickness of the protective film 16 is less than the thickness of the electrode fingers 23. The other configurations are the same as in Example 1, so their description is omitted.

[0047] Figure 7(b) is a cross-sectional view of the elastic wave device 180 according to Modification 8 of Example 1. As shown in Figure 7(b), in Modification 8 of Example 1, a protective film 16 is provided on the piezoelectric layer 15 so as to cover the electrode fingers 23. The thickness of the protective film 16 is greater than the thickness of the electrode fingers 23, and the upper surface of the protective film 16 is flattened. The other configurations are the same as in Example 1, so their description is omitted.

[0048] In modified examples 7 and 8 of Example 1, the protective film 16 is an inorganic insulating film such as a silicon oxide film or a silicon nitride film.

[0049] According to Example 1 and its modified form, the electrode finger 23 has a first layer 31 provided on the piezoelectric layer 15 and a second layer 32 provided on the first layer 31. The first layer 31 is a titanium aluminum nitride layer (TiAlN layer). The second layer 32 is a metal layer formed of a metal with a lower electrical resistivity than the first layer 31, such as an aluminum layer or an aluminum alloy layer. In this way, by providing the first layer 31, which is a TiAlN layer, between the piezoelectric layer 15 and the second layer 32, the power withstand capability can be improved and the TCF can be improved, as explained in Figures 3 and 4, because TiAlN has a high Young's modulus as shown in Table 1. Furthermore, despite having a high Young's modulus as shown in Table 1, TiAlN has a low density. Therefore, even if the thickness T1 of the first layer 31 varies due to manufacturing errors, the deviation of the resonant frequency and anti-resonant frequency from the desired value can be suppressed. Moreover, despite having a high Young's modulus and low density as shown in Table 1, TiAlN is conductive. Therefore, since the electrode fingers 23 can be formed using only conductive material, degradation of characteristics can be suppressed.

[0050] Furthermore, in Example 1 and its modified form, the first layer 31, which is a TiAlN layer, has an aluminum atom content of 20 to 50 atomic percent when the total amount of titanium and aluminum atoms is 100 atomic percent. Figure 8 is a binary phase diagram of titanium-aluminum. In Figure 8, the horizontal axis represents the aluminum atom content, and the vertical axis represents temperature. As shown in Figure 8, by setting the aluminum atom content to 20 to 50 atomic percent, the titanium-aluminum alloy contains the Ti3Al(α2) phase. The Ti3Al(α2) phase has excellent heat resistance. Therefore, in the first layer 31, it is preferable that the aluminum atom content is 20 to 50 atomic percent when the total amount of titanium and aluminum atoms is 100 atomic percent. From the viewpoint of obtaining the first layer 31 having excellent heat resistance and high-temperature strength, it is preferable that the titanium-aluminum alloy contains both the Ti3Al(α2) phase and the TiAl(γ) phase. Therefore, the proportion of aluminum atoms is preferably 33 atomic% or more and 49 atomic% or less, more preferably 34 atomic% or more and 48 atomic% or less, and even more preferably 35 atomic% or more and 47 atomic% or less.

[0051] Furthermore, in Example 1 and its modified form, the first layer 31, which is a TiAlN layer, has a nitrogen atom content of 10 atomic percent or more when the total amount of titanium atoms, aluminum atoms, and nitrogen atoms is set to 100 atomic percent. This increases the Young's modulus of the first layer 31. Therefore, it is possible to improve the power withstand capability and TCF. From the viewpoint of increasing the Young's modulus, the nitrogen atom content is preferably 15 atomic percent or more, more preferably 20 atomic percent or more, and even more preferably 30 atomic percent or more. Since an increase in the nitrogen atom content can lead to an increase in electrical resistance, the nitrogen atom content is preferably 60 atomic percent or less, more preferably 55 atomic percent or less, and even more preferably 50 atomic percent or less.

[0052] Furthermore, in Example 1 and its modified form, the second layer 32 is an aluminum layer or an aluminum alloy layer. This makes it possible to reduce the electrical resistance of the electrode finger 23. Thus, in order for the second layer 32 to function as a low-resistance layer, it is sufficient that it be formed of a metal with a lower electrical resistivity than the first layer 31. In addition to an aluminum layer or an aluminum alloy layer, the second layer 32 may also be a copper layer or a copper alloy layer. If the second layer 32 is a copper layer, the second layer 32 may contain impurities other than copper, either intentionally or unintentionally. If the second layer 32 is a copper alloy layer, the second layer 32 may contain impurities other than copper and the metal elements that constitute the copper alloy, either intentionally or unintentionally. The copper content in the second layer 32 is, for example, 80 atomic% or more, and 90 atomic% or more.

[0053] Furthermore, in Example 1 and its modified form, the thickness T1 of the first layer 31 is 5% to 60% of the thickness T3 of the electrode finger 23. By setting the thickness T1 of the first layer 31 to this size, the power withstand capability and TCF can be improved, and the thinning of the thickness T2 of the second layer 32 is suppressed, thereby suppressing an increase in the electrical resistance of the electrode finger 23. From the viewpoint of improving power withstand capability and TCF, the thickness T1 of the first layer 31 is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more, of the thickness T3 of the electrode finger 23. From the viewpoint of suppressing an increase in the electrical resistance of the electrode finger 23, the thickness T1 of the first layer 31 is preferably 55% or less, more preferably 50% or less, and even more preferably 45% or less, of the thickness T3 of the electrode finger 23.

[0054] Furthermore, in Modification 1 of Example 1, as shown in Figure 5, the electrode finger 23 has a third layer 33 between the first layer 31 and the second layer 32, which is a titanium layer or titanium nitride layer and is thinner than the first layer 31 and the second layer 32. By providing the third layer 33, which is a titanium layer or titanium nitride layer, between the first layer 31 and the second layer 32, the adhesion between the first layer 31 and the second layer 32 can be improved. In addition, if the second layer 32 is an aluminum layer, an aluminum alloy layer, a copper layer, or a copper alloy layer, the third layer 33 being thinner than the first layer 31 and the second layer 32 can suppress an increase in the electrical resistance of the electrode finger 23. [Examples]

[0055] Example 1 shows an example where the first layer 31 is a titanium aluminum nitride layer, while Example 2 shows an example where the first layer 31 is a chromium aluminum nitride layer, a chromium nitride layer, a diamond-like carbon layer, or a titanium carbide nitride layer. The other configurations of the elastic wave device according to Example 2 are the same as those of Example 1 or its modified counterparts, so their description is omitted.

[0056] Here, we show the results of measuring the resistance and density of each film formed on a silicon substrate using CrAlN (chromium aluminum nitride), CrN (chromium nitride), DLC (diamond-like carbon), and TiCN (titanium carbide nitride) layers. The Young's modulus is shown as a literature value, and the speed of sound is a value calculated using density and Young's modulus. The CrAlN layer measurement was taken when the proportion of aluminum atoms was 50-70 atomic percent when the total of chromium and aluminum atoms was set to 100 atomic percent, and the proportion of nitrogen atoms was 50 atomic percent when the total of chromium, aluminum, and nitrogen atoms was set to 100 atomic percent. The CrN layer measurement was taken when the proportion of nitrogen atoms was 50 atomic percent when the total of chromium and nitrogen atoms was set to 100 atomic percent. The TiCN layer measurement was taken when the proportion of titanium atoms was 50 atomic percent when the total of titanium, carbon, and nitrogen atoms was set to 100 atomic percent, and the proportion of carbon atoms (carbon atoms / (carbon atoms + nitrogen atoms)) to the total of carbon atoms and nitrogen atoms was 50%.

[0057] CrAlN layer Resistance: 2.8 MΩ·nm Density: 3.68~4.50g / cm 3 Young's modulus: 300-350 GPa Sound speed: 5064~6048m / s CrN layer Resistance: 4000Ω·nm Density: 5.9g / cm 3 Young's modulus: 300-400 GPa Sound speed: 4422~5106m / s DLC layer Resistance value: 10 7 ~10 14 Ω·cm Density: 2.0~2.8g / cm 3 Young's modulus: 200-1000 GPa Sound speed: 4688~10483m / s TiCN layer Resistance: 200Ω·nm Density: 5.0~5.5g / cm 3 Young's modulus: 300-650 GPa Sound speed: 4580~7071m / s

[0058] The Young's modulus of the CrAlN layer is 300-350 GPa, the Young's modulus of the CrN layer is 300-400 GPa, the Young's modulus of the DLC layer is 200-1000 GPa, and the Young's modulus of the TiCN layer is 300-650 GPa. Thus, the Young's moduli of the CrAlN layer, CrN layer, DLC layer, and TiCN layer are as large as those of the TiAlN layer. Therefore, in Example 2, by using a chromium aluminum nitride layer, a chromium nitride layer, a diamond-like carbon layer, or a titanium carbide nitride layer for the first layer 31, the power resistance can be improved and the TCF can be improved, similar to Example 1.

[0059] When the first layer 31 is a chromium aluminum nitride layer, from the viewpoint of ensuring a high Young's modulus, the proportion of aluminum atoms when the total of chromium atoms and aluminum atoms is 100 atomic percent is preferably 20 atomic percent or more and 50 atomic percent or less, more preferably 25 atomic percent or more and 45 atomic percent or less, and even more preferably 30 atomic percent or more and 40 atomic percent or less. From the viewpoint of ensuring a high Young's modulus, when the total of chromium atoms, aluminum atoms and nitrogen atoms is 100 atomic percent, the proportion of nitrogen atoms when the total of chromium atoms, aluminum atoms and nitrogen atoms is 100 atomic percent is preferably 30 atomic percent or more and 60 atomic percent or less, more preferably 35 atomic percent or more and 55 atomic percent or less, and even more preferably 40 atomic percent or more and 50 atomic percent or less.

[0060] When the first layer 31 is a chromium nitride layer, from the viewpoint of ensuring a high Young's modulus, the proportion of nitrogen atoms when the total amount of chromium atoms and nitrogen atoms is 100 atomic%, is preferably 30 atomic% or more and 60 atomic%, more preferably 35 atomic% or more and 55 atomic%, and even more preferably 40 atomic% or more and 50 atomic%.

[0061] When the first layer 31 is a titanium carbide nitride layer, from the viewpoint of ensuring a high Young's modulus, the proportion of titanium atoms, when the total of titanium atoms, carbon atoms, and nitrogen atoms is set to 100 atomic%, is preferably 40 atomic% or more and 70 atomic%, more preferably 45 atomic% or more and 65 atomic%, and even more preferably 50 atomic% or more and 60 atomic%, respectively. From the viewpoint of ensuring a high Young's modulus, the proportion of carbon atoms to the total of carbon atoms and nitrogen atoms (carbon atoms / (carbon atoms + nitrogen atoms)) is preferably 50% or more and 70%, more preferably 54% or more and 66%, and even more preferably 58% or more and 62%. [Examples]

[0062] Figure 9(a) is a circuit diagram of the filter 200 according to Embodiment 3. As shown in Figure 9(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 can be an elastic wave device according to Embodiment 1 and its modified form. The number of series resonators and parallel resonators can be set as appropriate. A ladder filter is shown as an example of the filter, but a multimode filter may also be used.

[0063] Figure 9(b) is a circuit diagram of a duplexer 210 according to a modified example of Embodiment 3. As shown in Figure 9(b), a transmit filter 50 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 52 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 50 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 52 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 50 and the receive filter 52 can be the filter of Embodiment 2. A duplexer is shown as an example of a multiplexer, but a triplexer or quadplexer may also be used.

[0064] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0065] 10...Substrate, 11...Insulating layer, 12...Insulating layer, 13...Insulating layer, 15...Piezoelectric layer, 16...Protective film, 20...Elastic wave resonator, 21...IDT, 22...Comb-type electrode, 23...Electrode fingers, 24...Busbar, 25...Reflector, 26...Crossing region, 30...Conductive film, 31...First layer, 32...Second layer, 33...Third layer, 40...Titanium layer, 41...Titanium aluminum alloy layer, 42...Titanium nitride layer, 43...Titanium aluminum nitride layer, 44...Aluminum copper alloy layer, 45a~45d...Conductive film, 50...Transmitting filter, 52...Receiving filter, 100, 110, 120, 130, 140, 150, 160, 170, 180...Elastic wave device, 200...Filter, 210...Duplexer

Claims

1. Piezoelectric layer and An elastic wave device comprising a pair of comb-shaped electrodes including electrode fingers, each having a first layer provided on the piezoelectric layer and being a titanium aluminum nitride layer, a chromium aluminum nitride layer, a chromium nitride layer, a diamond-like carbon layer, or a titanium carbide nitride layer, and a second layer provided on the first layer and being a metal layer formed of a metal with lower electrical resistivity than the first layer.

2. The elastic wave device according to claim 1, wherein the first layer is a titanium aluminum nitride layer, and the proportion of aluminum atoms is 20 atomic percent or more and 50 atomic percent or less when the total amount of titanium atoms and aluminum atoms is 100 atomic percent.

3. The elastic wave device according to claim 1 or 2, wherein the first layer is a titanium aluminum nitride layer, and the proportion of nitrogen atoms is 10 atomic percent or more when the total amount of titanium atoms, aluminum atoms, and nitrogen atoms is 100 atomic percent.

4. The elastic wave device according to claim 1 or 2, wherein the second layer is an aluminum layer, an aluminum alloy layer, a copper layer, or a copper alloy layer.

5. The elastic wave device according to claim 1 or 2, wherein the thickness of the first layer is 5% or more and 60% or less of the thickness of the electrode finger.

6. The electrode finger has a third layer that is thinner than the first and second layers between the first and second layers, The second layer is an aluminum layer, an aluminum alloy layer, a copper layer, or a copper alloy layer. The elastic wave device according to claim 1 or 2, wherein the third layer is a titanium layer or a titanium nitride layer.

7. A filter comprising the elastic wave device according to claim 1 or 2.

8. A multiplexer comprising the filter described in claim 7.

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